Propylene polymerization and deactivation processes with isoselective {cp/flu} zirconocene catalysts
Résumé
Industrially relevant single‐site precatalysts used to produce isotactic polypropylene (iPP) include C2‐symmetric {SBI} and C1‐symmetric {Cp/Flu} complexes of group 4 metals. While the latter can produce iPPs with a higher degree of isotacticity, they also suffer from poor productivity com-pared to their {SBI} counterparts. Several causes for this trend have been suggested—2,1‐Regioinser-tions are frequently pointed out, as they are suspected to drive the catalyst into a dormant state. While this event does not seem to significantly impact the productivity of {SBI} systems, the influence of these regioerror is poorly documented for isoselective {Cp/Flu} precatalysts. To address this issue, new Ph2X(Cp)(Flu) (Ph2X = Ph2C, FluC, Ph2Si) proligands (2a–k) and some of the correspond-ing dichlorozirconocenes (3a–h,k) were synthesized. These new compounds were characterized and tested in homogeneous propylene polymerization at 60 °C and the amounts of regioerrors in the resulting polymers were examined by13C NMR spectroscopy. A possible correlation between poor productivity and a high number of regioerrors was investigated and is discussed. Further-more, a C‐H activation process in the bulky nBu3C substituent upon activation of 4c (the dimethyl-ated analog of 3c) by B(C6F5)3 has been evidenced by NMR; DFT calculations support this C‐H activation as a deactivation mechanism. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
Domaines
Chimie
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